Skin CD4⁺ Trm cells distinguish acute cutaneous lupus erythematosus from localized discoid lupus erythematosus/subacute cutaneous lupus erythematosus and other skin diseases

Highlights

• Inappropriate activation of Trm cells was recently indicated to be involved in the pathogenesis of local immune disorders.

• Among CLE patients, patients with ACLE have the lowest CD4⁺ Trm cells and AIM2 expression level in CD4⁺ Trm cells compared with localized DLE and SCLE.

• CD4⁺ Trm cells show different distribution in different inflammatory skin diseases.

• AIM2 in CD4⁺ Trm cells can serve as a promising biomarker in discriminating ACLE from localized DLE and SCLE.

Abstract

Background

Although the contribution of aberrant CD4⁺ T cell signaling to systemic lupus erythematosus (SLE) is well established, its role in cutaneous lupus erythematosus (CLE) skin is largely unknown. Because the rate of systemic manifestations varies in each subtype, resident memory CD4⁺ T cells in lesions that are responsible for only skin-associated tissue responses may vary in each subtype. However, the role of CD4⁺ tissue-resident memory T (CD4⁺ Trm) cells in each CLE subtype remains unclear.

Objectives

To analyze and compare CD4⁺ Trm cells and absent in melanoma 2 (AIM2) identified by smart RNA sequencing (Smart-seq) in CD4⁺ Trm cells from patients with acute CLE (ACLE), subacute CLE (SCLE), and localized discoid lupus erythematosus (localized DLE) lesions.

Methods

We performed Smart-seq to investigate differences in dermal CD4⁺ Trm cells between patients with ACLE and normal controls (NCs). Multicolor immunohistochemistry was utilized to measure the levels of AIM2 in CD4⁺ Trm cells present in the skin of 134 clinical patients, which included patients with localized DLE (n = 19), ACLE (n = 19), SCLE (n = 16), psoriasis (n = 12), rosacea (n = 17), lichen planus (n = 18), and annular granuloma (n = 15), as well as NCs (n = 18).

Results

The Smart-seq data showed higher AIM2 expression in skin CD4⁺ Trm cells from ACLE lesions than NCs (fold change >10, adjusted P < 0.05). AIM2 expression in CD4⁺ Trm cells did not vary according to age or sex. AIM2 expression in CD4⁺ Trm cells was significantly lower in patients with ACLE (6.38 ± 5.22) than localized DLE (179.41 ± 160.98, P < 0.0001) and SCLE (63.43 ± 62.27, P < 0.05). In an overall comparison of ACLE with localized DLE and SCLE, the receiver operating characteristic curve for AIM2 expression in CD4⁺ Trm cells had a sensitivity of 100.00% and a specificity of 82.86% at a cutoff value of 18.26. In a comparison of ACLE with localized DLE, the sensitivity was 89.47%, and the specificity was 100.00% at a cutoff value of 12.26. In a comparison of ACLE with SCLE, the sensitivity was 100.00%, and the specificity was 75.00% at a cutoff value of 18.26.

Conclusions

The number of CD4⁺ Trm cells is increased in lesions of SCLE and localized DLE compared to ACLE, suggesting that CD4⁺ Trm cells may have a more crucial role in persistent lesions of SCLE and localized DLE. In addition, AIM2 expression in CD4⁺ Trm cells discriminates patients with ACLE from those with localized DLE and SCLE.

Introduction

Cutaneous lupus erythematosus (CLE) is an autoimmune disease that presents as a localized skin disease or a skin manifestation that appears in 70–80% of patients with systemic lupus erythematosus (SLE) [1]. CLE-specific skin lesions are subdivided into acute CLE (ACLE), subacute CLE (SCLE), and chronic CLE (CCLE). The main CCLE variant is chronic discoid lupus erythematosus (CDLE), which is further subdivided into localized DLE (localized DLE: affecting the skin of the head and face) or disseminated DLE (disseminated DLE: affecting the skin above and below the neck) [1]. The incidence of organ involvement varies among patients with different subtypes of CLE. Notably, ACLE has the highest incidence of systemic involvement (∼90%), whereas the damage caused by localized DLE is always restricted to the skin [2,3].

In patients with SLE, the rituximab response in cutaneous manifestations varies in different subtypes of lesions. Specifically, in patients with ACLE, dermatological improvement was imparted by anti-B cell therapies, while patients with SCLE and CCLE showed poor responses to B cell depletion [4]. Surprisingly, flares of SCLE and CCLE were observed in several patients with ACLE or without skin diseases, while other organ systems simultaneously responded well to rituximab treatment [4]. Hence, ACLE may be more strongly correlated with B cell signaling and abnormal CD4⁺ T follicular helper cells that induce the production of various autoantibodies. Abatacept, which inhibits T cell activation, was beneficial in some patients with refractory SLE but worsened the DLE lesions in a patient with refractory SLE [5]. In addition, abatacept is also reported to induce SCLE in individual case [6]. These findings suggest potential immunopathogenic differences across CLE subtypes. As recent studies have revealed that tissue-resident memory T (Trm) cells are involved in the duration of psoriasis, chronic intestinal inflammation, and vitiligo [[7], [8], [9], [10], [11]], Trm cells in skin lesions of CLE may provide an explanation for the immunopathogenic differences across CLE subtypes.

Tissue-resident memory T (Trm) cells, which are defined by the expression of CD69 and/or CD103, permanently reside in the skin and rapidly trigger cognate pathogen-derived local inflammatory responses [12,13]. To date, memory T cells presenting in different tissues show tissue specificity during protection or pathological processes [14,15]. As Trm cells are long-lived, resistant to damaging factors and possess a sustainable proinflammatory advantage, inappropriate activation of Trm cells may result in immunopathology and prolonged disease duration at the same location [16], and optimal treatment designed to completely silence Trm cells is required for the complete remission of the diseases [[17], [18], [19]].

In this study, we performed Smart-seq to analyze the gene expression profiles of CD4⁺ Trm cells in the skin of NCs and patients with ACLE. Furthermore, multicolor immunohistochemistry was used to reveal the number and distribution of CD4⁺ Trm cells in lesions of localized DLE, SCLE, ACLE, and other inflammatory skin diseases. Our data revealed that CD4⁺ Trm cells from NCs and patients with ACLE shared distinct transcriptional properties. Multicolor immunohistochemistry indicated an increased number of CD4⁺ Trm cells in patients with localized DLE and SCLE, but not patients with ACLE, compared to NCs.